Plasma processing apparatus and plasma processing method with a carrier wave group generating unit

ABSTRACT

A plasma processing apparatus includes a processing vessel; a carrier wave group generating unit configured to generate a carrier wave group including multiple carrier waves having different frequencies belonging to a preset frequency band centered around a predetermined center frequency; and a plasma generating unit configured to generate plasma within the processing vessel by using the carrier wave group.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a U.S. national phase application under 35 U.S.C. §371 of PCT Application No. PCT/JP2016/063926 filed on May 10, 2016,which claims the benefit of Japanese Patent Application No. 2015-097520filed on May 12, 2015, the entire disclosures of which are incorporatedherein by reference.

TECHNICAL FIELD

The various embodiments described herein pertain generally to a plasmaprocessing apparatus and a plasma processing method.

BACKGROUND ART

There is known a plasma processing apparatus using excitation of aprocessing gas by a microwave. For example, this plasma processingapparatus generates plasma by radiating the microwave generated by amicrowave oscillator into a processing vessel and ionizing theprocessing gas within the processing vessel.

Further, as a technique for suppressing a deflection of an electricfield which occurs within the processing vessel and is caused by astanding wave of the microwave, there is known a technique of generatinga microwave having a preset frequency bandwidth by modulating afrequency of a carrier wave.

Patent Document 1: Japanese Patent Laid-open Publication No. 2012-109080

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the aforementioned prior art, however, it is yet to be considered tosuppress a mode jump and non-uniformity of a plasma density.

In the prior art, the microwave having the preset frequency bandwidth isgenerated by modulating the frequency of the carrier wave. Here, thougha frequency of the microwave generated by the frequency modulationchanges within the preset frequency bandwidth with a lapse of time, thismicrowave exists as a frequency component having a single frequency at acertain time point.

In case of generating the plasma by using the microwave which serves asthe frequency component having the single frequency, the microwave isabsorbed into the plasma most efficiently when the frequency of themicrowave is adjusted to a frequency at which a power of a reflectionwave becomes minimum (hereinafter, referred to as “minimum reflectionfrequency”). However, if the microwave is absorbed with the highefficiency, a plasma density is increased, so that the minimumreflection frequency is then shifted to a higher frequency. Once theminimum reflection frequency is shifted, a power of the microwaveabsorbed into the plasma is reduced unless the frequency thereof ischanged. As a result, the plasma density is decreased. If the plasmadensity is decreased, the minimum reflection frequency is shifted to alower frequency. As a result, the power of the microwave absorbed intothe plasma is increased, which leads to the increase of the plasmadensity. In the prior art, as the increase and the decrease of theplasma density are repeated, the non-uniformity of the plasma densitywould be increased. Besides, in the prior art, there may occur a modejump which is a phenomenon that the plasma density becomes momentarilydiscontinuous due to a change in a plasma mode.

Means for Solving the Problems

In an exemplary embodiment, a plasma processing apparatus includes aprocessing vessel; a carrier wave group generating unit configured togenerate a carrier wave group including multiple carrier waves havingdifferent frequencies belonging to a preset frequency band centeredaround a predetermined center frequency; and a plasma generating unitconfigured to generate plasma within the processing vessel by using thecarrier wave group.

Effect of the Invention

According to the exemplary embodiments of the plasma processingapparatus, it is possible to suppress the occurrence of the mode jumpand the non-uniformity of the plasma density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a plasma processingapparatus according to an exemplary embodiment.

FIG. 2 is a diagram for describing an example of a method of generatinga carrier wave group.

FIG. 3A is a diagram illustrating an example of a waveform of a carrierwave group

FIG. 3B is a diagram illustrating the example of the waveform of thecarrier wave group.

FIG. 3C is a diagram illustrating the example of the waveform of thecarrier wave group.

FIG. 3D is a diagram illustrating the example of the waveform of thecarrier wave group.

FIG. 4 is a diagram for describing suppression of non-uniformity in aplasma density by the carrier wave group.

FIG. 5 is a diagram for describing a problem caused when using amicrowave having a single frequency.

FIG. 6 is a diagram for describing a mechanism of suppressing thenon-uniformity in the plasma density by the carrier wave group accordingto the exemplary embodiment.

FIG. 7 is a flowchart for describing a plasma processing methodaccording to the exemplary embodiment.

FIG. 8 is a diagram showing a variation of a plasma density whengenerating plasma by using a carrier wave group or a microwave having asingle frequency.

FIG. 9 is a diagram showing a relationship between a plasma density anda power of a progressive wave of a microwave when generating plasma byusing a microwave having a single frequency.

FIG. 10 is a diagram showing a relationship between a plasma density anda power of a progressive wave of a carrier wave group when generatingplasma by using the carrier wave group.

FIG. 11A is a diagram illustrating an example of a relationship betweena carrier wave pitch and a number of multiple carrier waves belonging tothe carrier wave group.

FIG. 11B is a diagram illustrating a variation of a power of the carrierwave group absorbed into plasma in relation to a variation of thecarrier wave pitch.

FIG. 11C is a diagram showing an example of a relationship between acarrier wave pitch and an emission intensity of the plasma.

FIG. 12 is a diagram showing an example of a waveform of another carrierwave group.

FIG. 13 is a diagram showing an example of a waveform of at least onecarrier wave.

DETAILED DESCRIPTION

In the following, a plasma processing apparatus according to anexemplary embodiment will be described in detail. In the variousdrawings, same or corresponding parts will be assigned same referencenumerals.

FIG. 1 is a diagram schematically illustrating a plasma processingapparatus according to the exemplary embodiment. A plasma processingapparatus 1 shown in FIG. 1 is equipped with a processing vessel 12, astage 14, a carrier wave group generating unit 16, an antenna 18, adielectric window 20 and a control unit 100.

The processing vessel 12 has therein a processing space S for performinga plasma processing therein. The processing vessel 12 has a sidewall 12a and a bottom 12 b. The sidewall 12 a has a substantially cylindricalshape. Hereinafter, an imaginary axis line X extended at a center of thecylindrical shape of the sidewall 12 a is set, and an extensiondirection of the axis line X is defined as an axis line X direction. Thebottom 12 b is provided at a lower end of the sidewall 12 a and closes abottom opening of the sidewall 12 a. The bottom 12 b is provided with anexhaust hole 12 h for gas exhaust. An upper end of the sidewall 12 a isopened.

An upper end opening of the sidewall 12 a is closed by the dielectricwindow 20. An O-ring 19 is provided between the dielectric window 20 andthe upper end of the sidewall 12 a. The dielectric window 20 is providedat the upper end of the sidewall 12 a with the O-ring 19 therebetween.The O-ring 19 allows the processing vessel 12 to be sealed airtightly.The stage 14 is accommodated in the processing space S, and a processingtarget object W is placed on the stage 14. The dielectric window 20 hasa facing surface 20 a which faces the processing space S.

The carrier wave group generating unit 16 is configured to generate acarrier wave group including multiple carrier waves having differentfrequencies belonging to a preset frequency band centered around apredetermined center frequency. By way of example, the carrier wavegroup generating unit 16 has a PLL (Phase Locked Loop) oscillatorconfigured to oscillate a microwave having a phase synchronized with areference frequency; and an IQ digital modulator connected to the PLLoscillator. The carrier wave group generating unit 16 sets a frequencyof the microwave oscillated from the PLL oscillator as the centerfrequency. Further, the carrier wave group generating unit 16 generatesthe carrier wave group by generating, with the IQ digital modulator, themultiple carrier waves having the different frequencies belonging to thepreset frequency band centered around the frequency of the microwavewhich is set as the center frequency. For example, if inverse Fouriertransform is performed on N number of complex data symbols andcontinuous signals are generated, the carrier wave group of the presentdisclosure can be generated. This signal generation method may beimplemented by the same method as an OFDMA (OrthogonalFrequency-Division Multiple Access) modulation method for use in digitaltelevision broadcasting or the like (see, for example, Japanese PatentNo. 5,320,260). Further, the center frequency and the frequency band ofthe carrier wave group generated by the carrier wave group generatingunit 16 are controlled by the control unit 100 to be described later.

FIG. 2 is a diagram for describing an example of a method of generatingthe carrier wave group. In FIG. 2, waveform data is a sequence ofpreviously digitized codes. Waveform data X(t) at a certain time point tis represented by the following expression (1).X(t)=A(t)cos(ωt+θ ₀)  (1)

Here, A(t) means an amplitude at the certain time point t, and θ₀denotes an initial phase.

By developing the expression (1) using addition theorem, the followingexpression (2) is drawn.X(t)=A(t)cos ωt·cos θ₀ −A(t)sin ωt·sin θ₀  (2)

In-phase component data (I data) I(t) of the waveform data X(t) isrepresented by the following expression (3). Further, quadraturecomponent data (Q data) Q(t) of the waveform data X(t) is represented bythe following expression (4).I(t)=A(t)cos θ₀  (3)Q(t)=A(t)cos θ₀  (4)

The following expression (5) is drawn from the expressions (2) to (4).X(t)=I(t)cos ωt−Q(t)sin ωt  (5)

The above expression (5) implies that all waveform data X(t) can beexpressed by using the I data I(t) and the Q data Q(t).

In the carrier wave group generating unit 16, by quantizing the waveformdata X(t) and performing inverse Fourier transform thereon, the I dataI(t) and the Q data Q(t) are separated. Then, each of the I data I(t)and the Q data Q(t) is D/A (Digital/Analog)-converted and is inputted toa low pass filter (LPF) which allows only a low frequency component topass therethrough. Meanwhile, two reference carrier waves cos ωt and−sin ωt having a phase difference of 90° are generated from a referencecarrier wave (e.g., a microwave) having a center frequency fo generatedfrom the PLL oscillator. Then, by modulating the reference carrier wavescos ωt and −sin ωt having the phase difference of 90° with the I dataI(t) and the Q data Q(t) output from the LPF, a carrier wave group isgenerated. That is, by multiplying the I data I(t) by the referencecarrier wave cos ωt and the Q data Q(t) by the reference carrier wave−sin ωt and then by adding the two multiplication results, the carrierwave group is generated. In the present exemplary embodiment, thecarrier wave group is obtained by multiplexing a carrier wave with apitch of 10 kHz and a bandwidth of 40 MHz by using a microwave having acenter frequency of 2450 MHz. By setting the phases of neighboringcarrier waves to be orthogonal (different by 90°), a large number ofclosest carrier waves can be arranged.

Here, a waveform of the carrier wave group generated by the carrier wavegroup generating unit 16 will be explained. FIG. 3A to FIG. 3D arediagrams illustrating an example of the waveform of the carrier wavegroup. FIG. 3A shows the waveform of the carrier wave group in athree-dimensional coordinate space formed by a time axis, a frequencyaxis and an amplitude axis. FIG. 3B shows the waveform of the carrierwave group in a two-dimensional coordinate space formed by the frequencyaxis and the amplitude axis. FIG. 3C shows the waveform of the carrierwave group in a two-dimensional coordinate space formed by the time axisand the frequency axis. FIG. 3D shows the waveform of the carrier wavegroup in a two-dimensional coordinate space formed by the time axis andthe amplitude axis.

As depicted in FIG. 3A to FIG. 3D, the carrier wave group is composed ofmultiple carrier waves f₁ to f₁₂ having different frequencies belongingto a preset frequency band (e.g., 40 MHz) centered around apredetermined center frequency (e.g., 2.45 GHz). The frequency of eachcarrier wave is maintained constant regardless of a lapse of time.Further, the multiple carrier waves have the same amplitude. Theamplitude of each carrier wave is maintained constant regardless of alapse of time. Moreover, among the multiple carrier waves, at least twocarrier waves having neighboring frequencies in the preset frequencyband have a phase difference of 90°. For example, the phases of thecarrier wave f₁ and the carrier wave f₂ having neighboring frequenciesmay be different by 90°. Furthermore, the frequencies of the multiplecarrier waves are arranged at a regular interval (e.g., 10 kHz) withinthe preset frequency band.

As in the exemplary embodiment, by generating the carrier wave groupcomposed of the multiple carrier waves, a frequency of any one of themultiple carrier waves belonging to the carrier wave group may beallowed to coincide with a frequency at which a power of the reflectionwave of the carrier wave group becomes minimum (hereinafter, referred toas “minimum reflection frequency”). As a result, according to thepresent exemplary embodiment, since a power of the carrier wave groupabsorbed into plasma can be maintained substantially constant, thenon-uniformity of the plasma density can be suppressed.

FIG. 4 is a diagram for describing suppression of the non-uniformity ofthe plasma density by the carrier wave group. In FIG. 4, a horizontalaxis represents a frequency [GHz], and a vertical axis indicates a power[dBm]. Further, in FIG. 4, a graph 501 shows a frequency spectrum of aprogressive wave of the carrier wave group, and a graph group 502indicates a frequency spectrum of a reflection wave of the carrier wavegroup. Moreover, in FIG. 4, as experimental conditions, a processing gasand a flow rate are Cl₂/Ar=100 sccm/300 sccm, and a pressure is set tobe 140 mTorr.

As shown in the graph 501 and the graph group 502 of FIG. 4, in case ofgenerating the carrier wave group having the multiple carrier waves, afrequency of any one of the multiple carrier waves belonging to thecarrier wave group coincides with the minimum reflection frequency.Accordingly, the power of the carrier wave group absorbed into plasma ismaintained substantially constant. In the example of FIG. 4, the powerof the carrier wave group absorbed into the plasma corresponds to anarea of a region surrounded by the graph 501 and the graph group 502.Here, an area of a region surrounded by the graph 501 and one graph 502a of the graph group 502 is defined as A1, and an area of a regionsurrounded by the graph 501 and one graph 502 b of the graph group 502is defined as A2. The areas A1 and A2 are substantially equal, whichindicates that the power of the carrier wave group absorbed into theplasma is maintained substantially constant regardless of the change ofthe minimum reflection frequency. As a result, since the decrease of theplasma density is suppressed, the non-uniformity of the plasma densityis also suppressed.

Here, a mechanism of suppressing the non-uniformity of the plasmadensity by the carrier wave group according to the present exemplaryembodiment will be described in detail. Prior to explaining thismechanism of suppressing the non-uniformity of the plasma density by thecarrier wave group according to the present exemplary embodiment, aproblem that might be caused when using a microwave having a singlefrequency will be first explained as a premise. FIG. 5 is a diagram fordescribing a problem caused when using a microwave having a singlefrequency. In FIG. 5, a graph 511 shows a portion of a frequencyspectrum of a reflection wave of the microwave corresponding to theminimum reflection frequency.

As depicted in FIG. 5, in case of using a microwave f₁′ having a singlefrequency, the single frequency of the microwave f₁′ is fixed tocoincide with the minimum reflection frequency. If so, the power of themicrowave f₁′ absorbed into the plasma is increased, which leads to anincrease of the plasma density. If the plasma density is increased, theminimum reflection frequency is deviated from the single frequency ofthe microwave f₁′, as indicated by a solid-line arrow of FIG. 5.Accordingly, the reflection wave of the microwave f₁′ is increased. Ifthe reflection wave of the microwave f₁′ is increased, the power of themicrowave f₁′ absorbed into the plasma is reduced, which results in adecrease of the plasma density. If the plasma density is decreased, thereflection wave of the microwave f₁′ is reduced, so that the minimumreflection frequency gents closer to the single frequency of themicrowave f₁′, as indicated by a dashed-line arrow of FIG. 5. In such acase, the power of the microwave f₁′ absorbed into the plasma isincreased, resulting in the increase of the plasma density again. Thus,when using the microwave f₁′ having the single frequency, thenon-uniformity of the plasma density may be increased as the increaseand the decrease of the plasma density are repeated. Furthermore, incase of using a microwave having a preset frequency bandwidth generatedby modulating the frequency of the carrier wave, the non-uniformity ofthe plasma density may also be increased as this microwave has a singlefrequency at a certain time point.

Meanwhile, a mechanism of suppressing the non-uniformity of the plasmadensity by the carrier wave group according to the exemplary embodimentwill be discussed. FIG. 6 is a diagram for describing the mechanism ofsuppressing the non-uniformity of the plasma density by the carrier wavegroup according to the exemplary embodiment. In FIG. 6, a graph 512shows a portion of a frequency spectrum of the reflection wave of thecarrier wave group corresponding to the minimum reflection frequency.

As shown in FIG. 6, when using a carrier wave group including themultiple carrier waves (carrier waves f₁, f₂, f₃, . . . ) having thedifferent frequencies, a frequency of any one of the multiple carrierwaves belonging to the carrier wave group coincides with the minimumreflection frequency. In the example of FIG. 6, it is assumed that afrequency of a carrier wave f₁ among the multiple carrier wavesbelonging to the carrier wave group coincides with the minimumreflection wave. If so, a power of the carrier wave f₁ absorbed into theplasma is increased, resulting in an increase of the plasma density. Ifthe plasma density increases, the minimum reflection frequency isdeviated from the frequency of the carrier wave f₁, as shown by asolid-line arrow of FIG. 6. The minimum reflection frequency deviatedfrom the frequency of the carrier wave f₁ coincides with a frequency ofa carrier wave f₂. Accordingly, a power of the carrier wave f₂ absorbedinto the plasma is increased, which leads to the increase of the plasmadensity. Thus, if the carrier wave group including the multiple carrierwaves having the different frequencies is used, the repetition of theincrease and the decrease of the plasma density is avoided. As a result,the non-uniformity of the plasma density is suppressed.

Referring back to FIG. 1, the plasma processing apparatus 1 furtherincludes an amplifier 21, a waveguide 22, a dummy load 23, a detector(progressive wave) 24, a detector (reflection wave) 25, a tuner 26, amode converter 27 and a coaxial waveguide 28.

The carrier wave group generating unit 16 is connected to the waveguide22 via the amplifier 21. The amplifier 21 is configured to amplify thecarrier wave group generated by the carrier wave group generating unit16 and output the amplified carrier wave group to the waveguide 22. Thewaveguide 22 may be, but not limited to, a rectangular waveguide. Thewaveguide 22 is connected to the mode converter 27, and the modeconverter 27 is connected to an upper end of the coaxial waveguide 28.

The dummy load 23 is connected to the waveguide 22 via a circulator 23a. The circulator 23 a is configured to extract the reflection wave ofthe carrier wave group reflected from the processing vessel 12 andoutput the extracted reflection wave of the carrier wave group to thedummy load 23. The dummy load 23 converts the reflection wave of thecarrier wave group input from the circulator 23 a to heat by a load orthe like.

The detector (progressive wave) 24 is connected to the waveguide 22 viaa directional coupler 24 a. The directional coupler 24 a is configuredto extract the progressive wave of the carrier wave group heading towardthe processing vessel 12 and output the extracted progressive wave ofthe carrier wave group to the detector (progressive wave) 24. Thedetector (progressive wave) 24 is configured to detect the frequencyspectrum of the progressive wave of the carrier wave group input fromthe directional coupler 24 a and output the detected frequency spectrumof the progressive wave of the carrier wave group to the control unit100.

The detector (reflection wave) 25 is connected to the waveguide 22 via adirectional coupler 25 a. The directional coupler 25 a is configured toextract the reflection wave of the carrier wave group reflected from theprocessing vessel 12 and output the extracted reflection wave of thecarrier wave group to the detector (reflection wave) 25. The detector(reflection wave) 25 is configured to detect the frequency spectrum ofthe reflection wave of the carrier wave group input from the directionalcoupler 25 a and output the detected frequency spectrum of thereflection wave of the carrier wave group to the control unit 100.

The tuner 26 is provided at the waveguide 22 and has a function ofmatching impedances between the carrier wave group generating unit 16and the processing vessel 12. The tuner 26 has movable plates 26 a and26 b configured to be protrusible into a space within the waveguide 22.The tuner 26 matches the impedance between the carrier wave groupgenerating unit 16 and the processing vessel 12 by controllingprotruding positions of the movable plates 26 a and 26 b with respect toa reference position.

The coaxial waveguide 28 is extended along the axis line X. The coaxialwaveguide 28 includes an outer conductor 28 a and an inner conductor 28b. The outer conductor 28 a has a substantially cylindrical shapeextended in the axis line X direction. The inner conductor 28 b isprovided within the outer conductor 28 a. This inner conductor 28 b hasa substantially cylindrical shape extended along the axis line X.

The carrier wave group generated by the carrier wave group generatingunit 16 is transmitted to the mode converter 27 through the tuner 26 andthe waveguide 22. The mode converter 27 is configured to convert a modeof the carrier wave group and supply the mode-converted carrier wavegroup to the coaxial waveguide 28. The carrier wave group from thecoaxial waveguide 28 is supplied to the antenna 18.

The antenna 18 is configured to radiate a carrier wave group for plasmaexcitation based on the carrier wave group generated by the carrier wavegroup generating unit 16. The antenna 18 has a slot plate 30, adielectric plate 32 and a cooling jacket 34. The antenna 18 is providedon a surface 20 b of the dielectric window 20 opposite from the facingsurface 20 a, and radiates the carrier wave group for plasma excitationinto the processing space S through the dielectric window 20 based onthe carrier wave group generated by the carrier wave group generatingunit 16.

The slot plate 30 is formed to have a substantially circular plate shapehaving a plate surface orthogonal to the axis line X. The slot plate 30is placed on the surface 20 b of the dielectric window 20 opposite fromthe facing surface 20 a with the plate surface thereof aligned to thatof the dielectric window 20. The slot plate 30 is provided with amultiple number of slots 30 a arranged in a circumferential directionwith respect to the axis line X. The slot plate 30 is of a typeconstituting a radial line slot antenna. The slot plate 30 is made of ametal having conductivity and has the substantially circular plateshape. The slot plate 30 is provided with the multiple number of slots30 a. Further, formed at a central portion of the slot plate 30 is athrough hole 30 d through which a conduction line 36 to be describedlater can be inserted.

The dielectric plate 32 has a substantially circular plate shape havinga plate surface orthogonal to the axis line X. The dielectric plate 32is provided between the slot plate 30 and a lower surface of the coolingjacket 34. The dielectric plate 32 is made of, by way of non-limitingexample, quartz and has the substantially circular plate shape.

A surface of the cooling jacket 34 has conductivity. A flow path 34 athrough which a coolant flows is provided within the cooling jacket 34.The dielectric plate 32 and the slot plate 30 are cooled by the flow ofthe coolant. A lower end of the outer conductor 28 a is electricallyconnected to an upper surface of the cooling jacket 34. Further, a lowerend of the inner conductor 28 b is electrically connected to the slotplate 30 through holes formed at central portions of the cooling jacket34 and the dielectric plate 32.

The carrier wave group from the coaxial waveguide 28 is propagated tothe dielectric plate 32 and then introduced from the slots 30 a of theslot plate 30 into the processing space S through the dielectric window20. In the exemplary embodiment, the conduction line 36 passes throughan inner hole of the inner conductor 28 b of the coaxial waveguide 28.The through hole 30 d is formed at the central portion of the slot plate30, and the conduction line 36 is inserted through the through hole 30d. The conduction line 36 is extended along the axis line X and isconnected to a gas supply system 38.

The gas supply system 38 is configured to supply a processing gas forprocessing the processing target object W into the conduction line 36.The gas supply system 38 may include a gas source 38 a, a valve 38 b anda flow rate controller 38 c. The gas source 38 a is a source of theprocessing gas. The valve 38 b switches a supply and a stop of thesupply of the processing gas from the gas source 38 a. The flow ratecontroller 38 c may be implemented by, for example, a mass flowcontroller and is configured to control a flow rate of the processinggas from the gas source 38 a. Further, the gas supply system 38corresponds to an example of a gas supply device configured to introducethe processing gas for use in a plasma reaction into the processingspace S.

In the present exemplary embodiment, the plasma processing apparatus 1is further equipped with an injector 41. The injector 41 is configuredto supply the gas from the conduction line 36 into a through hole 20 hof the dielectric window 20. The gas supplied into the through hole 20 hof the dielectric window 20 is introduced into the processing space S.In the following description, a gas supply path formed by the conductionline 36, the injector 41 and the through hole 20 h may sometimes bereferred to as “central gas introduction unit”.

The stage 14 is provided to face the dielectric window 20 in the axisline X direction. This stage 14 is provided such that the processingspace S is formed between the dielectric window 20 and the stage 14. Theprocessing target object W is placed on the stage 14. In the presentexemplary embodiment, the stage 14 includes a table 14 a, a focus ring14 b and an electrostatic chuck 14 c. The stage 14 corresponds to anexample of a mounting table.

The table 14 a is supported by a cylindrical supporting member 48. Thecylindrical supporting member 48 is made of an insulating material andis extended from the bottom 12 b vertically upwards. Further, aconductive cylindrical support member 50 is provided on an outer surfaceof the cylindrical supporting member 48. The cylindrical support member50 is extended from the bottom 12 b of the processing vessel 12vertically upwards along the outer surface of the cylindrical supportingmember 48. An annular exhaust path 51 is formed between the cylindricalsupport member 50 and the sidewall 12 a.

An annular baffle plate 52 having a multiple number of through holes isprovided of an upper portion of the exhaust path 51, and an exhaustdevice 56 is connected to a lower portion of the exhaust hole 12 h viaan exhaust line 54. The exhaust device 56 has an automatic pressurecontrol valve (APC) and a vacuum pump such as a turbo molecular pump.The processing space S within the processing vessel 12 can bedecompressed to a required vacuum level by the exhaust device 56.

The table 14 a also serves as a high frequency electrode. The table 14 ais electrically connected to a high frequency power supply 58 for a RFbias via a power feed rod 62 and a matching unit 60. The high frequencypower supply 58 is configured to output, at a preset power level, a highfrequency power (hereinafter, appropriately referred to as “bias power”)having a preset frequency of, e.g., 13.65 MHz suitable for controllingenergy of ions attracted into the processing target object W. Thematching unit 60 incorporates therein a matching device configured tomatch an impedance of the high frequency power supply 58 and animpedance at a load side thereof such as, mainly, the electrode, theplasma and the processing vessel 12. The matching device includes ablocking capacitor for self-bias generation.

An electrostatic chuck 14 c is provided on a top surface of the table 14a. The electrostatic chuck 14 c is configured to hold the processingtarget objet W by an electrostatic attracting force. The focus ring 14 bis provided at an outside of the electrostatic chuck 14 c in adiametrical direction to surround the processing target object Wannularly. The electrostatic chuck 14 c includes an electrode 14 d, aninsulating film 14 e and an insulating film 14 f. The electrode 14 d ismade of a conductive film and is embedded between the insulating film 14e and the insulating film 14 f. The electrode 14 d is electricallyconnected to a high voltage DC power supply 64 via a switch 66 and acoated line 68. The electrostatic chuck 14 c is configured to attractand hold the processing target object W by a Coulomb force generated bya DC voltage applied from the DC power supply 64.

An annular coolant path 14 g is provided within the table 14 a and isextended in a circumferential direction. A coolant of a presettemperature, for example, cooling water is supplied into and circulatedthrough the coolant path 14 g from a chiller unit (not shown) throughpipelines 70 and 72. A top surface temperature of the electrostaticchuck 14 c is controlled by the temperature of the coolant. Further, aheat transfer gas, for example, a He gas is supplied into a gap betweena top surface of the electrostatic chuck 14 c and a rear surface of theprocessing target object W through a gas supply line 74, and atemperature of the processing target object W is controlled based on thetop surface temperature of the electrostatic chuck 14 c.

In the plasma processing apparatus 1 having the above-describedconfiguration, the gas is introduced through the conduction line 36 andthe injector 41 and supplied into the processing space S from thethrough hole 20 h of the dielectric window 20 along the axis line X.Further, the carrier wave group is introduced into the processing spaceS and/or the through hole 20 h from the antenna 18 via the dielectricwindow 20. Accordingly, the plasma is generated in the processing spaceS and/or the through hole 20 h. Here, the antenna 18 and the dielectricwindow 20 are an example of a plasma generating unit configured togenerate the plasma within the processing vessel 12 by using the carrierwave group.

The control unit 100 is connected to the individual components of theplasma processing apparatus 1 and controls the individual components inan overall manner. The control unit 100 is equipped with a controller101 having a central processing unit (CPU), a user interface 102 and astorage unit 103.

The controller 101 controls overall operations of the individualcomponents such as the carrier wave group generating unit 16, the stage14, the gas supply system 38 and the exhaust device 56 by executing aprogram and a processing recipe stored in the storage unit 103.

The user interface 102 includes a keyboard or a touch panel throughwhich a process manager inputs a command to manage the plasma processingapparatus 1; a display configured to visually display an operationalstatus of the plasma processing apparatus 1; and so forth.

The storage unit 103 has stored thereon control programs (software) forimplementing various processings performed in the plasma processingapparatus 1 under the control of the controller 101; processing recipesin which processing condition data are recorded to allow a certainprocessing to be performed; and so forth. In response to an instructionfrom the user interface 102 or when necessary, the controller 101retrieves various control programs from the storage unit 103 andexecutes the retrieved control programs, so that the required processingis performed in the plasma processing apparatus 1 under the control ofthe controller 101. The control programs and the recipes such as theprocessing condition data may be used while being stored in acomputer-readable recording medium (e.g., a hard disk, a CD, a flexibledisk, a semiconductor memory, etc.), or may be used on-line by beingreceived from another apparatus through, for example, a dedicated line,whenever necessary.

Now, a plasma processing method using the plasma processing apparatus 1according to the exemplary embodiment will be explained. FIG. 7 is aflowchart for describing the plasma processing method according to theexemplary embodiment.

As depicted in FIG. 7, the carrier wave group generating unit 16 of theplasma processing apparatus 1 generates the carrier wave group includingthe multiple carrier waves having the different frequencies belonging tothe preset frequency band centered around a predetermined centerfrequency (process S101). Further, initial values of the centerfrequency and the frequency band of the carrier wave group generated bythe carrier wave group generating unit 16 are controlled by the controlunit 100.

The antenna 18 and the dielectric window 20 generate the plasma withinthe processing vessel 12 by using the carrier wave group (process S102).

The control unit 100 receives an input of the frequency spectrum of thereflection wave of the carrier wave group from the detector 25. Then,the control unit 100 determines, by controlling the carrier wave groupgenerating unit 16, a width of the preset frequency band such that theminimum reflection frequency, which refers to the frequency of thereflection wave corresponding to the minimum value of the frequencyspectrum, exists within the preset frequency band (process S103).

In case of carrying on the processing (process S104: No), the controlunit 100 returns the processing back to the process S101, whereas incase of finishing the processing (process S104: Yes), the control unit100 ends the processing.

Now, an effect (plasma density) attained by the plasma processingapparatus 1 according to the exemplary embodiment will be discussed.FIG. 8 is a diagram showing a variation of a plasma density when plasmais generated by using a carrier wave group or a microwave having asingle frequency. In FIG. 8, a horizontal axis represents a time [sec]and a vertical axis indicates an ion density [ions/cm³] as an example ofthe plasma density.

Furthermore, in FIG. 8, a graph 521 shows the variation of the plasmadensity when generating the plasma by using the microwave having thesingle frequency, and a graph 522 shows the variation of the plasmadensity when generating the plasma by using the carrier wave grouphaving a preset frequency bandwidth of 10 MHz in the plasma processingapparatus 1 according to the present exemplary embodiment. Further, agraph 523 shows the variation of the plasma density when generating theplasma by using the carrier wave group having a preset frequencybandwidth of 20 MHz in the plasma processing apparatus 1 according tothe present exemplary embodiment. A graph 524 shows the variation of theplasma density when generating the plasma by using the carrier wavegroup having a preset frequency bandwidth of 40 MHz in the plasmaprocessing apparatus 1 according to the present exemplary embodiment.Further, in the example of FIG. 8, as experiment conditions, theprocessing gas and the flow rate are Ar=100 sccm is used, and the powerof the progressive wave of the carrier wave group or the power of theprogressive wave of the microwave is set to be 1.4 kW.

As can be seen from FIG. 8, when the plasma is generated by using thecarrier wave group, the non-uniformity of the ion density (that is, theplasma density) is suppressed, as compared to the case where the plasmais generated by using the microwave having the single frequency.

Now, an effect (mode jump) achieved by the plasma processing apparatus 1according to the exemplary embodiment will be discussed. FIG. 9 is adiagram showing a relationship between the plasma density and the powerof the progressive wave of the microwave when generating the plasma byusing the microwave having the single frequency. FIG. 10 is a diagramshowing a relationship between the plasma density and the power of theprogressive wave of the carrier wave group when generating the plasma byusing the carrier wave group. In FIG. 9 and FIG. 10, a vertical axisrepresents the ion density [ions/cm³] which is an example of the plasmadensity. Further, in FIG. 9, a horizontal axis represents the power [W]of the progressive wave of the microwave. In FIG. 10, a horizontal axisindicates the power [W] of the progressive wave of the carrier wavegroup.

Furthermore, in FIG. 9 and FIG. 10, “X=0 mm” indicates the ion densitycorresponding to a center position “0” of the processing target objectW. Further, “X=150 mm” indicates the ion density corresponding to aposition “150 mm” away from the center position “0” of the processingtarget object W in a diametrical direction of the processing targetobject W. Further, “X=210 mm” indicates the ion density corresponding toa position “210 mm” away from the center position “0” of the processingtarget object W in the diametrical direction of the processing targetobject W.

As can be seen from FIG. 9, in the case of generating the plasma byusing the microwave having the single frequency, the mode jump which isa phenomenon that the ion density (i.e., plasma density) becomesmomentarily discontinuous is observed at three powers of the progressivewave of the microwave.

In contrast, as shown in FIG. 10, in the case of generating the plasmaby using the carrier wave group, the mode jump which is the phenomenonthat the ion density (i.e., plasma density) becomes momentarilydiscontinuous is observed at a single power of the progressive wave ofthe carrier wave group microwave. That is, as compared to the case ofgenerating the plasma by using the microwave having the singlefrequency, occurrence of the mode jump is suppressed when generating theplasma by using the carrier wave group.

Now, an effect (stability of plasma) obtained by the plasma processingapparatus 1 according to the present exemplary embodiment will beexplained. In the following, referring to FIG. 11A to FIG. 11C, anexperiment result showing an example of a relationship between aninterval of frequencies of the multiple carrier waves belonging to thecarrier wave group (hereinafter, referred to as “carrier wave pitch”)and stability of the plasma will be explained. FIG. 11A is a diagramshowing an example of a relationship between the carrier wave pitch anda number of the multiple carrier waves belonging to the carrier wavegroup. In FIG. 11A, the power of the carrier wave group, that is, a sumof powers of the individual carrier waves belonging to the carrier wavegroup is set to be constant. Furthermore, in FIG. 11A, the carrier wavegroup exists within the frequency band of 40 MHz centered around thecenter frequency of 2450 MHz.

As depicted in FIG. 11A, as the carrier wave pitch gets smaller, thenumber of the carrier waves belonging to the carrier wave groupincreases. For example, when the carrier wave pitch is 400 kHz, 100 kHz,40 kHz and 10 kHz, the number of the carrier waves belonging to thecarrier wave group is 100, 400, 1000 and 4000, respectively.

FIG. 11B is a diagram for describing the variation of the power of thecarrier wave group absorbed into the plasma in relation to the variationof the carrier wave pitch. In FIG. 11B, a horizontal axis represents thefrequency [GHz] and a vertical axis represents the power [dBm]. Further,in FIG. 11B, a graph 515 indicates the frequency spectrum of theprogressive wave of the carrier wave group. A graph 516 shows thefrequency spectrum of the reflection wave of the carrier wave group whenthe carrier wave pitch is 400 kHz. Further, a graph 517 shows thefrequency spectrum of the reflection wave of the carrier wave group whenthe carrier wave pitch is 100 kHz. A graph 518 shows the frequencyspectrum of the reflection wave of the carrier wave group when thecarrier wave pitch is 40 kHz. A graph 519 indicates the frequencyspectrum of the reflection wave of the carrier wave group when thecarrier wave pitch is 10 kHz. Furthermore, in FIG. 11B, as processingconditions, the processing gas of Cl₂ and Ar respectively having flowrates of 100 sccm and 300 sccm is used, and a pressure is set to be 140mTorr; the center frequency, 2.450 GHz; the frequency band, 40 MHz; andan input power of the progressive wave of the carrier wave group, 1.5kW.

As can be seen from FIG. 11B, when the carrier wave pitch is equal to orless than 100 kHz, an area of a region surrounded by the graph 515 andthe graph 517, 518 or 519, that is, a power of the carrier wave groupabsorbed into the plasma is maintained substantially constant.

FIG. 11C is a diagram showing an example of a relationship between thecarrier wave pitch and the emission intensity of the plasma. FIG. 11Cshows an experiment result of investigating a variation in the emissionintensity of the plasma with a lapse of time to evaluate the stabilityof the plasma. In FIG. 11C, a horizontal axis represents the time [sec]and a vertical axis represents the emission intensity [abu.] of theplasma. In FIG. 11C, a graph 531 shows the variation of the emissionintensity of the plasma generated by using the carrier wave group havingthe carrier wave pitch of 400 kHz. A graph 532 shows the variation ofthe emission intensity of the plasma generated by using the carrier wavegroup having the carrier wave pitch of 100 kHz. A graph 533 shows thevariation of the emission intensity of the plasma generated by using thecarrier wave group having the carrier wave pitch of 40 kHz. A graph 534shows the variation of the emission intensity of the plasma generated byusing the carrier wave group having the carrier wave pitch of 10 kHz.

As can be clearly seen from the experiment result of FIG. 11C, as thecarrier wave pitch is reduced, the variation of the emission intensityof the plasma over time is suppressed. That is, by setting the carrierwave pitch to be small, the stability of the plasma can be improved.

As stated above, in the plasma processing apparatus 1 according to thepresent exemplary embodiment, since the carrier wave group including themultiple carrier waves is generated and the plasma is generated by usingthe carrier wave group, the repetition of the increase and the decreaseof the plasma density can be avoided. As a result, the non-uniformity ofthe plasma density and the occurrence of a mode jump can be suppressed.

Furthermore, in the plasma processing apparatus 1 according to thepresent exemplary embodiment, the width of the preset frequency band isset such that the minimum reflection frequency exists within the presetfrequency band of the carrier wave group. As a consequence, thepossibility that the minimum reflection frequency coincides with thefrequency of any one reflection wave among the reflection wavesbelonging to the carrier wave group can be increased, so thatnon-uniformity of the plasma density and the occurrence of the mode jumpcan be further suppressed.

Modification Example 1

Now, a modification example 1 will be explained. A plasma processingapparatus according to the modification example 1 has the sameconfiguration as that of the plasma processing apparatus 1 according tothe above-described exemplary embodiment except that another carrierwave group different from the above-described carrier wave group isgenerated prior to performing the plasma processing. Thus, in themodification example 1, the same components as those of theabove-described exemplary embodiment will be assigned same referencenumerals, and detailed description thereof will be omitted.

In the plasma processing apparatus according to the modification example1, the carrier wave group generating unit 16 generates an additionalcarrier wave group prior to performing the plasma processing on theprocessing target object by the plasma which is generated by using thecarrier wave group. Like the carrier wave group (hereinafter, referredto as “carrier wave group for plasma processing”) for use in the plasmaprocessing, this additional carrier wave group includes multiple carrierwaves having different frequencies belonging to a preset frequency bandcentered around a predetermined center frequency. An amplitude of eachof the carrier waves belonging to this additional carrier wave groupvaries with a lapse of time, and a maximum value of this amplitude islarger than the amplitude of each carrier wave belonging to the carrierwave group for plasma processing.

The antenna 18 and the dielectric window 20 generate plasma within theprocessing vessel 12 by using this additional carrier wave group. Thisadditional carrier wave group is used for ignition of the plasma.

Here, a waveform of the additional carrier wave group generated by thecarrier wave group generating unit 16 will be explained. FIG. 12 is adiagram illustrating an example of the waveform of the additionalcarrier wave group. FIG. 12 shows the waveform of the additional carrierwave group in the three-dimensional coordinate space formed by the timeaxis, the frequency axis and the amplitude axis.

As depicted in FIG. 12, the additional carrier wave group includesmultiple carrier waves f₁ to f₉ having different frequencies belongingto the preset frequency band (e.g., 40 MHz) centered around thepredetermined center frequency (e.g., 2.45 GHz). An amplitude of eachcarrier wave belonging to this additional carrier wave group varies witha lapse of time, and a maximum value of this amplitude is larger thanthe amplitude of each carrier wave belonging to the carrier wave groupfor plasma processing. In the example of FIG. 12, the amplitudes of thecarrier waves f₁ to f₉ reach their maximum values at different timepoints within a processing time of an ignition process. Further, themaximum values of the amplitudes of the carrier waves f1 to f9 arelarger than the amplitude of each carrier wave belonging to the carrierwave group for plasma processing.

In the plasma processing apparatus according to the modification example1, the additional carrier wave group including the multiple carrierwaves is generated prior to performing the plasma processing, and theplasma is generated by using this additional carrier wave group.Therefore, the ignition of the plasma can be performed stably.

Modification Example 2

Now, a modification example 2 will be explained. A plasma processingapparatus according to the modification example 2 has the sameconfiguration as that of the plasma processing apparatus 1 according tothe above-described exemplary embodiment except that at least one of themultiple carrier waves belonging to the carrier wave group is generatedprior to performing the plasma processing. Thus, in the modificationexample 2, the same components as those of the above-described exemplaryembodiment will be assigned same reference numerals, and detaileddescription thereof will be omitted.

In the plasma processing apparatus according to the modification example2, the carrier wave group generating unit 16 generates at least one ofthe multiple carrier waves belonging to the carrier wave group prior toperforming the plasma processing on the processing target object by theplasma generated by using the carrier wave group.

The antenna 18 and the dielectric window 20 generate the plasma withinthe processing vessel 12 by using the at least one carrier wavegenerated. This at least one carrier wave is used for ignition of theplasma.

Here, a waveform of the at least one carrier wave generated by thecarrier wave group generating unit 16 will be explained. FIG. 13 is adiagram illustrating an example of the waveform of the at least onecarrier wave. FIG. 13 shows the waveform of another carrier wave groupin the three-dimensional coordinate space formed by the time axis, thefrequency axis and the amplitude axis.

As depicted in FIG. 13, an amplitude of at least one carrier wave f₅ islarger than an amplitude of the carrier wave f₅ for a time during whichthe plasma processing is performed.

In the plasma processing apparatus according to the modification example2, the at least one carrier wave among the multiple carrier wavesbelonging to the carrier wave group is generated before the plasmaprocessing is performed, and the plasma is generated by using the atleast one carrier wave. Therefore, the ignition of the plasma can beperformed stably.

Furthermore, the exemplary embodiment has been described for the examplecase of using the microwave. However, the same effects can be achievedwhen using high frequency plasma of 13.56 MHz and VHF plasma of 100 MHzas well. That is, the exemplary embodiment is not merely limited tousing the microwave.

EXPLANATION OF REFERENCE NUMERALS

-   -   1: Plasma processing apparatus    -   12: Processing vessel    -   14: Stage    -   16: Carrier wave group generating unit    -   18: Antenna    -   20: Dielectric window    -   30: Slot plate    -   38: Gas supply system    -   100: Control unit    -   101: Controller    -   102: User interface    -   103: Storage unit

We claim:
 1. A plasma processing apparatus, comprising: a processingvessel; a carrier wave group generating unit configured to generate acarrier wave group including multiple carrier waves having differentfrequencies belonging to a preset frequency band centered around apredetermined center frequency; and a plasma generating unit configuredto generate plasma within the processing vessel by using the carrierwave group, wherein a number of the multiple carrier waves belonging tothe carrier wave group is 400 or more.
 2. The plasma processingapparatus of claim 1, wherein the frequencies of the multiple carrierwaves are arranged at a regular interval.
 3. The plasma processingapparatus of claim 1, wherein the carrier wave group is generated bymodulating carrier waves having a phase difference of 90° with I dataand Q data obtained by quantizing waveform data and performing inverseFourier transform thereon.
 4. The plasma processing apparatus of claim1, wherein the frequencies of the multiple carrier waves are maintainedconstant regardless of a lapse of time.
 5. The plasma processingapparatus of claim 1, wherein the multiple carrier waves have a sameamplitude.
 6. The plasma processing apparatus of claim 1, wherein, amongthe multiple carrier waves, at least two carrier waves havingneighboring frequencies in the preset frequency band have differentphases.
 7. The plasma processing apparatus of claim 1, wherein, amongthe multiple carrier waves, at least two carrier waves havingneighboring frequencies in the preset frequency band have a phasedifference of 90°.
 8. The plasma processing apparatus of claim 1,wherein the carrier wave group generating unit generates an additionalcarrier wave group including multiple carrier waves having differentfrequencies belonging to the present frequency band centered around thepredetermined center frequency prior to performing a plasma processingon a processing target object by the plasma, the plasma generating unitgenerates the plasma within the processing vessel by using theadditional carrier wave group, and an amplitude of each of the multiplecarrier waves belonging to the additional carrier wave group varies witha lapse of time, and a maximum value of the amplitude of each of themultiple carrier waves belonging to the additional carrier wave group islarger than an amplitude of each of the multiple carrier waves belongingto the carrier wave group.
 9. The plasma processing apparatus of claim1, wherein the carrier wave group generating unit generates at least onecarrier wave among the multiple carrier waves belonging to the carrierwave group prior to performing a plasma processing on a processingtarget object by the plasma, the plasma generating unit generates theplasma within the processing vessel by using the at least one carrierwave, and an amplitude of the at least one carrier wave is larger thanan amplitude of the at least one carrier wave for a time during whichthe plasma processing is performed.
 10. A plasma processing apparatus,comprising: a processing vessel; a carrier wave group generating unitconfigured to generate a carrier wave group including multiple carrierwaves having different frequencies belonging to a preset frequency bandcentered around a predetermined center frequency; and a plasmagenerating unit configured to generate plasma within the processingvessel by using the carrier wave group, wherein the amplitude of each ofthe multiple carrier waves is maintained constant regardless of a lapseof time.
 11. A plasma processing apparatus, comprising: a processingvessel; a carrier wave group generating unit configured to generate acarrier wave group including multiple carrier waves having differentfrequencies belonging to a preset frequency band centered around apredetermined center frequency; a plasma generating unit configured togenerate plasma within the processing vessel by using the carrier wavegroup; a detector configured to detect a frequency spectrum of areflection wave of the carrier wave group; and a control unit configuredto determine a width of the present frequency band by controlling thecarrier wave group generating unit such that a minimum reflectionfrequency, which is a frequency of the reflection wave corresponding toa minimum value of the frequency spectrum, exists within the presetfrequency band.
 12. A plasma processing method, comprising: generating acarrier wave group including multiple carrier waves having differentfrequencies belonging to a preset frequency band centered around apredetermined center frequency; and generating plasma within aprocessing vessel by using the carrier wave group, wherein a number ofthe multiple carrier waves belonging to the carrier wave group is 400 ormore.